Magnetar May Hold Clues to the Mystery of Fast Radio Bursts

Astronomers are investigating a radio-burst emission from a magnetar that reactivated last year, and have so far found that its burst activity is both strong and narrow. They suspect that further study of the burst could reveal new information about fast radio bursts. 

Magnetars are neutron stars with extremely strong magnetic fields (over a quadrillion times stronger than Earth's magnetic field). Scientists first spotted the magnetar XTE J1810−197 after an X-ray outburst in 2003, and in 2004, researchers detected a radio emission from the source. The magnetar produced the first transient radio emission ever detected by scientists. But after a few years of emitting variable radio emissions, the magnetar went quiet in 2008. 

XTE J1810−197 reactivated last year in December 2018. Scientists detected a bright, pulsed radio signal at 1.52 gigahertz (GHz) coming from the magnetar, the second radio outburst observed from this source. A strange and exciting observation, scientists launched an investigation of the object, studying it at low radio frequencies using the Giant Metrewave Radio Telescope (GMRT). 

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The team, led by Yogesh Maan of the Netherlands Institute for Radio Astronomy, found that radio bursts from this magnetar are between 1.0 and 4.0 ms wide at 650 megahertz (MHz). They also found that this width narrows at 1,360 MHz. The team also observed that the magnetar's magnitude of brightness has rapidly decreased since the burst was detected in 2018. So not only is the recent burst activity of XTE J1810−197 relatively narrow, it is also relatively strong, the researchers found. 

"The bursts exhibit spectral structures which cannot be explained by interstellar propagation effects," the team of astronomers wrote in the paper describing their findings, which was published Aug. 12 in the preprint journal arXiv, stating that the bursts from XTE J1810−197 don't disseminate in space as expected.

"While the spectral structures are particularly noticeable in the early phases of the outburst, these seem to be less prominent as well as less frequent in the later phases, suggesting an evolution of the underlying cause of these spectral structures.

"These structures might indicate a phenomenological link with the repeating fast radio bursts which also show interesting, more detailed frequency structures," the astronomers added. 

The team plans to investigate the emission from XTE J1810−197 further at higher frequencies. They hope that this will answer their question of whether the magnetar is somehow linked to repeating fast radio bursts. 

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